1. Field of the Invention
The present invention relates to an optical amplifier which can optically amplify a signal light having a plurality of wavelengths of signal light together in an optical transmission system, and a method of controlling such an optical amplifier.
2. Related Background Art
An optical amplifier includes an optical waveguide, doped with a fluorescent material excitable with pumping light, for optically amplifying signal light, and pumping means for supplying the pumping light to the optical waveguide; and is disposed in a repeater station in an optical transmission system, or the like.
The optical amplifier disclosed in Reference 1, S. Kinoshita, et al., "Wide-dynamic-Range WDM Optical Fiber Amplifiers for 32.times.10 Gb/s, SMF Transmission Systems," OSA TOPS Vol. 25, pp. 280-283 (1998), is provided with an optical attenuator having a variable amount of attenuation, in order to adjust its gain while maintaining a flatness in gain. On the other hand, the optical amplifier disclosed in Reference 2, M. J. Yadlowsky, "EDFA without dynamic gain tilt using excite-state trapping," OSA TOPS Vol. 25, pp. 24-27 (1998), is provided with a light source for outputting control light (having a wavelength of 977.5 nm) which brings a fluorescent material (Er element) to its excited level, separately from an pumping light source for outputting pumping light (having a wavelength of 1470 nm), in order to adjust its gain while maintaining a flatness in gain.